Coating compositions that are applied to automobile bodies or like coated objects are required to provide excellent coating film performance in terms of scratch resistance, acid resistance, stain resistance, finished appearance, etc.
Hitherto, melamine crosslinking coating compositions have been widely used as coating compositions for such objects to be coated, i.e. coated objects. A melamine crosslinking coating composition contains a hydroxyl group-containing resin and a melamine resin that acts as a crosslinking agent. Since the melamine crosslinking coating composition has a high crosslinking density during heat curing, the coating film formed therefrom has excellent coating film performance such as scratch resistance, finished appearance, etc. However, the melamine crosslinkage in this coating composition easily undergoes hydrolysis by acid rain; therefore, this coating composition provides unsatisfactory acid resistance.
Patent Literature 1 discloses a two-package type urethane crosslinking coating composition comprising a hydroxyl group-containing acrylic resin, a hydroxyl group-containing oligoester, and an isocyanate prepolymer. The urethane crosslinkage in this coating composition hardly undergoes hydrolysis; therefore, the coating film formed from this coating composition has excellent acid resistance. However, the scratch resistance of this coating film is not satisfactory.